How 3D printers made a motorcycle, skis and snowboard

3D printer maker Stratasys and auto/aerospace parts maker TE Connectivity have been busy on separate projects to demonstrate the possibilities for large 3D-printed parts to be used in commercial applications, and the companies showed a rideable motorcycle and working skis and snowboard.

The 3D printed motorcycle created by TE Connectivity to prove to its engineers that polymers can withstand great amounts of stress. The bike is styled after a Harley Davison softwail and can do a whopping 15mph with two riders.

When it comes to 3D printing, the general public is likely unaware how far the technology has come from the days when making figurines and trinkets was about all many believed the machines could do.

Because of advancements in hard and soft thermoplastic polymers, metal sintering techniques and printing software and hardware platforms, 3D printing machines are capable of producing a wide variety of objects that can withstand a great deal of force.

That was TE Connectivity's goal when it used 3D printing to build a working motorcycle. The company, which makes electronic connectivity and sensor equipment for the automotive, aerospace and defense industries, wanted to prove to its 7,500 engineers that 3D printing was up to the task of creating working production parts.

The motorcycle, whose design harkens back to a classic Harley Davidson Softail, took 1,000 hours to build and had so many parts that TE Connectivity principal engineer Charles Fry lost count of how many there actually were.

The motorcycle weighs 250 lbs. and can easily accommodate two riders. The bike has been tested with weights of up to 400 lbs., and while its tiny 750-watt, 1hp electric motor strains under that kind of load, it can easily transport a person of average weight up to 15mph for more than two minutes, Fry said.

The cost to build: $25,000.

While that may seem expensive, it's only because it's the first working motorcycle to be almost completely made with 3D printing.

The motorcycle's frame is primarily made through fused deposition modeling (FDM), where an extruder head controlled by a robotic mechanism lays down layer after layer of melted polymer. The polymers consisted of common ABS (acrylonitrile butadiene styrene) filament and Ultem 9085 resin, which is heat resistant.

Additionally, metal parts on the bike, such as the headlight assembly, were made of bronze using direct laser sintering (DMLS) 3D printing. DMLS systems lay down a fine layer (typically 20-micron thick) of powdered metal across a build area. A laser then sketches out a pattern in the powder, melting or fusing many individual powder layers together. The DMLS process creates a highly dense material with a finished surface.

The metal components of the bike are coated with polished nickel.

Perhaps most remarkable about the belt-drive bike was the printed rear-wheel hub; it was created using FDM as one part, sprocket gear, bearings and all.

"You can't build it by any other method," Fry said. "It uses a herring bone gear, and there's no way to get the herring bone gear into the assembly once the bearings are built."

Even the bearings are plastic, which Fry said have held up to the heat and stress of more than 20 miles of riding. "The bearings proved to be very rugged," he said.

Aside from the motor, which was purchased separately, the only parts of the bike that weren't printed were its belt drive, side mirrors and its kickstand, Fry said. Those parts were afterthoughts, and the mirrors were added for bling and the kickstand for convenience when showing the motorcycle.

Building a large object like a motorcycle doesn't come without some major frustrations, including 3D printers that malfunctioned, power outages that shut down a print midway through, and misprints that forced engineers to go back to the drawing board.

"It took us 150 to 170 hours of build time for the frame," Fry said. "As we got halfway through some prints, they'd fail; that can really add time to the build."

An odd speed bump in the build process was created by residual solvent left behind after being used to remove an extensive amount of support material left over from the 3D-printing process. Support scaffolding is often printed to hold up parts with gaps and projecting cantilevers until printing is finished. Then the support material is either cut away or dissolved using solvents.

The solvent fluid would settle in nooks and crannies of the motorcycle and continue to weep from the bike for weeks, often fouling finishing operations and leaving streaking on the surface of parts.

Fry said he learned the hard way to meticulously clean the solvent from bike and finishing processes.

3D printing your snow sports

Like TE Connectivity, industrial 3D printer maker Stratasys had something to prove when its Skunkworks division set out to manufacture working skis and a snowboard.

Dominic Mannella, a senior applications engineer with Stratasys Skunkworks, said the one thing he didn't have to concern himself with was designing the skis or snowboard.

There is, what Mannella called, a "vibrant" online DIY ski community, and he was able to find all the plans he needed to construct the skis from CAD drawings.

The only part not printed were the skis' bindings.

The skis, modeled after ones from the snow sports company K2, took 120 hours to print. As with all ski bottoms, a slippery layer of P-Tex (polyethylene) became the base on which all other layers were added.

The center, and the thickest layer of the skis, were printed on an enormous Stratasys Fortis 900c 3D printer using an FDM process extruding Ultem 9085 polymer filament. The Ultem is strong and resists moisture, Mannella said. The skis required 50 layers of Ultem to complete.

The 170 centimeter skis couldn't fit into a single printer, so they were produced in two parts -- front and rear. Additionaly a metal edge was applied so that, as with every ski, the edge can carve turns in the snow.

The various layers of materials -- the P-Tex, four layers of Ultem and the metal edges -- were clamped together and bound using a 24-hour drying epoxy.

"A day later, you pull the clamps off... and you have a fully laminated ski," Mannella said.

The skis were tested at Lake Tahoe in Nevada by Stratasys CEO David Reis, and they performed nearly as well as top-of-the-line commercial skis, Mannella said.

The task was more difficult than the skis because the snowboard turned out to be more complex to build, Johnson said.

The board was made entirely from Ultem 9085 polymer filament. Johnson had intended to use a printable nylon to create the board's bindings, but chose instead to simply purchase bindings to make the build go faster.

While creating a snowboard that must have more flexibility than skis was difficult, Johnson said one advantage even over traditional manufacturing is the ability to manipulate a myriad of variables. For example, the board's length, weight, camber, and stiffness can all be manipulated independent of each other through the printer's CAD software.

By using the semi-porous Ultem 9085, Johnson was able to simply wax the board instead of using P-Tex polymer for the base.

The snowboard took three days to print, and it was produced in three layers, all bound together by epoxy. A metal edge, like the skis, was also added post printing.

Next up for Stratasys' Skunkworks, according to Mannella? You guessed it: ski boots.

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